The long-term objective is to examine the anatomy of central nervous system mechanisms that control middle ear aeration. Preliminary studies support our hypothesis of neural connections between the middle ear, eustachian tube and brain analogous to the neural circuits that monitor and regulate aeration in the lung. This project will address two basic questions: What are the total inputs from the middle ear to the brain and do they change in the developing animal? What are the total outputs from the brain to the eustachian tube muscles, and do they also change with age? To do this, we will (1) determine the projections from the tympanic plexus nerves to the nucleus of the solitary tract with horseradish peroxidase (HRP) in the adult monkey, (2) determine the motor and proprioceptive innervation of the eustachian tube muscles with HRP in the adult monkey, and (3) compare the number, size and ratio of the myelinated and unmyelinated fibers in these nerves in the developing and adult monkey using degeneration techniques with electron microscopy. A demonstrated mechanism for neural control of middle ear aeration would have profound implications for the understanding of middle ear physiology and would be directly relevant to the clinical problem of otitis media. (In the USA, otitis media is the most commonly diagnosed childhood disease, is the reason for the two most common surgical procedures on children, and incurs health care costs of $2 billion annually). The concepts and specific objectives outlined in this proposal are a complete departure from past and present approaches to otitis media, and have not been examined previously. We will explore this new approach using established neuroanatomic methods.